1. Field of the Invention
The present invention generally relates to methods and systems for sampling defects for electron beam review by separating defects detected on a wafer into bins based on combined attributes from optical inspection and optical review and sampling the defects from the bins to generate a defect sample for the electron beam review.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail.
Information beyond simple defect detection is often generated during inspection processes. For example, the detected defects are often classified into different groups. In one such example, after finding defects, they may be classified into different groups based on the defect characteristics such as size, magnitude, and location. In one particular example, using the information generated by optical wafer inspection, defects may be separated into cleanable and non-cleanable defects.
Defect classification often cannot be performed based on just images or information generated by a wafer inspection tool. In these instances, additional information may be generated using a defect review tool and defect classification is then determined based on the additional information. In some such instances, defects found by an optical defect finding apparatus may be reviewed using a high resolution scanning electron microscope (SEM) review tool. Defect review may, however, also be performed using an optical-based system. For example, laser-based defect review may be performed to verify a defect population detected by optical inspection.
In some instances, the optical review verified defect population may then be transferred to electron beam defect review. However, optical review is generally not capable of generating DOI type information for the verified defects. For instance, optical review may be capable of separating real defects from non-real defects (or “nuisances”), but not necessarily determining any DOI information for the real defects. Therefore, based on optical defect review results, the electron beam review tool may have no a priori knowledge of the nature of the defects included in the defect population to be reviewed.
In addition, as described above, an optical inspector may perform some defect classification that provides classification results (e.g., defect paretos), but those classification results generally have substantially limited accuracy and purity, particularly for defects that are near the threshold separating one defect classification from another. Therefore, any defect classification result generated by optical inspection may be provided to a defect review tool, but those defect classification results may not be particularly useful. Furthermore, the limited accuracy of defect classifications generated by optical inspection classifiers can result in ineffective troubleshooting of process tool excursions.
Electron beam based defect review that is performed using information generated by optical inspection or optical review may, therefore, have a number of disadvantages. For example, due to the limited information provided by optical inspection and optical review, electron beam review performed based on that information may have relatively low capture rates of actual defects. In addition, it would be difficult, if not impossible, to perform targeted DOI sampling for electron beam based defect review based on the defect information that is provided by optical inspection and optical review. Therefore, electron beam based review will take a relatively long time to produce ground truth defect classification results (e.g., ground truth paretos).
Accordingly, it would be advantageous to develop methods and systems for generating a defect sample for electron beam review that do not have one or more of the disadvantages described above.